The present invention relates to information storage system transducers. It is well known in the field of magnetic information storage systems that a means for increasing storage density and signal resolution is to reduce the separation between a transducer and associated media. For many years, devices incorporating flexible media, such as floppy disk or tape drives, have employed a head in contact with the flexible media during operation in order to reduce the head-media spacing. Recently, hard disk drives have been designed which can operate with high-speed contact between the hard disk surface and the head.
Another means for increasing signal resolution that has become increasingly icommon is the use of magneto resistive (MR) or other sensors for a head. MR elements may be used along with inductive writing elements, or may be separately employed as sensors. While MR sensors offer greater sensitivity than inductive transducers, they are more prone to damage from high-speed contact with a hard disk surface, and may also suffer from corrosion. For these reasons, air bearing surfaces (ABS) for heads containing MR sensors are conventionally coated with a hard, durable carbon or carbon-based overcoat. During etching of the ABS that creates relieved features for interacting with the rapidly moving media surface, the MR sensors are covered with a mask.
The overcoats may be formed before or after etching of the ABS. Current methods for making ABS overcoats include sputtering or ion beam chemical vapor deposition (IBCVD) to form diamond-like carbon (DLC) films. More recently, cathodic arc deposition has been used to form tetrahedral-amorphous carbon (ta-C) films having even greater hardness. Employment of harder films allows the thickness of the films to be reduced, which can help to reduce head-media spacing.
DLC and ta-C films have a high stress as well as high hardness, and do not adhere well to slider ABS or magnetic layers, and so an adhesion layer of Si or Si3N4 is conventionally formed to help with stress relief and adhesion. The DLC coating 20 conventionally has a thickness that is about four times that of the adhesion layer. Thus a 80 xc3x85 layer of DLC may be formed on a 20 xc3x85 adhesion layer of Si3N4, to create a minimum head-media spacing of 100 xc3x85. Further head-media spacing conventionally occurs due to penetration of energetic interlayer ions into underlying magnetic layers, deadening a portion of those magnetic layers.
It is not clear that the minimum head-medium spacing due to these layers can be reduced substantially without encountering problems in overcoat durability and adhesion layer continuity. For example, a 10 xc3x85 adhesion layer may be only a few atoms thick, and may not provide adequate adhesion even if one assumes that the somewhat thicker carbon overcoat can withstand high-speed head-disk contact without damage or removal. Further, the possibility of corrosion may increase as conventional overcoats are made thinner, risking failure of the head.
In accordance with the present invention plural carbon-containing overcoats are formed on a media-facing surface of a head. The plural carbon-containing overcoats may serve to avoid corrosion without increasing head-media spacing. A first of the overcoats may be formed prior to creation of air bearing features on the media-facing surface, with a second overcoat formed after creation of air bearing features. The first overcoat may be etched back substantially or completely prior to formation of the second overcoat. The overcoats may be formed of several forms of diamond-like carbon (DLC) or silicon-carbide (SiC).